Natural gas is fast replacing oil and coal as a cleaner and low cost fuel. Particularly after the recent United States shale revolution, natural gas is now a major contributor to the energy landscape in the United States. Notwithstanding this development, the natural gas delivery infrastructure is rapidly aging in the United States.
The US Department of Energy has emphasized that ensuring the reliability of natural gas delivery systems is a critical need for the energy sector. With approximately 650,000 miles of delivery pipelines, efficient means are necessary to ensure the maintenance of these pipelines. A reliable and timely detection of failure of any part of the pipeline is critical to ensure the continued operation of the natural gas pipeline and its infrastructure.
Amongst the methods for inspecting pipelines are those used for detecting leaks in the pipeline. These range from manual inspection using trained dogs to advanced satellite based hyper spectral imaging. The various methods can be classified into non-optical and optical methods. The primary non-optical methods include acoustic monitoring, gas sampling, soil monitoring, flow monitoring and software based dynamic modeling.
Optical methods for leak detection can be classified as either passive or active. Active methods illuminate the area above the pipeline with a laser or a broadband source. The absorption or scattering caused by natural gas molecules above surface is monitored using an array of sensors at specific wavelengths. If there is a significant absorption or scattering above a pipeline, then a leak is presumed to exist. The basic techniques for active monitoring include Tunable Diode Laser Absorption Spectroscopy (TDLAS), Laser Induced Fluorescence (LIF), Coherent Anti-Raman Spectroscopy (CARS), Fourier Transform Infrared Spectroscopy (FTIR) and evanescent sensing.
Passive monitoring of natural gas leaks is similar to active monitoring in many aspects. However, the major difference between active and passive techniques is that passive techniques do not require a source. This makes passive systems less expensive. However, since a strong radiation source is not employed, many more expansive detectors and imagers have to be used with the passive systems. Two major types of passive systems used for monitoring leaks from natural gas pipelines are thermal imaging and multi-wavelength imaging.
The present invention provides for improved leak detection methods in natural gas pipelines.